One of the fundamental outcomes of the nuclear shell model is the prediction of "stability islands" in the domain of the hypothetical superheavy elements. Enhanced stability was expected for the deformed nuclei near Z=108 and N=162, yet much stronger effects have been predicted for heavier spherical nuclei close to the shells Z=114 and N=184, beyond the doubly-magic nucleus 208Pb (Z=82, N=126).
The talk is devoted to the experimental verification of these predictions -- the synthesis and study of both the decay and chemical properties of the superheavy elements.
For the synthesis of the heavy nuclei, fusion reactions of 208Pb, 209Bi target nuclei with 50Ti, 54Cr, and 70Zn projectiles (cold fusion) have been used. These allowed investigations of the decay of the nuclides with Z=104-113 and N=151-165 in the region of the deformed shells Z=108 and N=162. The synthesis of even heavier and more neutron-rich nuclei has been carried out in the fusion reactions of 233,238U, 237Np, 242,244Pu, 245,248Cm, and now 249Bk and 249Cf with 48Ca projectiles (hot fusion). These made it possible to study the decay of nuclides with Z=104-118 and the higher neutron numbers, N=161-177.
The decay properties of the 48 synthesized nuclei obtained in 48Ca- induced reactions present direct experimental evidence for the existence of the superheavy nuclei and considerably expand the Periodic Table of the chemical elements. Simultaneously, in the chemical studies of elements 112 and 114 by methods of absorption gas chromatography, the influence of "relativistic effects" on the chemical properties of the superheavy elements was observed for the first time.
The experiment on the synthesis of element 117 was performed recently by the FLNR (Dubna) - ORNL (Oak-Ridge) - Vanderbilt University (Nashville) - LLNL (Livermore) - IAR (Dimitrovgrad) collaboration. The results of the 48Ca-induced reactions leading to the other elements were obtained in FLNR (Dubna, Russia) as well in collaboration with LLNL (Livermore, USA), ORNL (Oak-Ridge) and PSI (Villigen, Switzerland), while the data from cold fusion reactions are from GSI (Darmstadt) and RIKEN (Tokyo).
Argonne Physics Division Colloquium Schedule